We have produced monoclonal antibodies that recognize three distinct non-overlapping domains within the heavy chain of smooth muscle myosin isolated from turkey gizzard: (1) a 50-kilodalton peptide derived by controlled proteolysis of subfragment-one (the globular head of myosin) previously found to be associated with actin-binding; (2) the carboxyterminus of subfragment-two; and (3) a trytic peptide of light meromyosin previously found to be associated with self-association of myosin into filaments.